Bro, it was literally said that Kyrex was pretending to be part of the relationship just so that he could continue having sex with Diego! Like I said, he was ma-ni-pu-la-ted. You're not wrong about Diego thinking they were in a relationship but Kyrex lied and confirmed it! Kyrex also didn't mention not wanting to be in a relationship to Diego at all, and he didn't reject him even though he knew he didn't want to! He just led him on!
I'm not gonna lie about the part that Diego is for a matter of fact lonely and desperate of a relationship, but rather than abusing Diego, he could've rejected him! Easy! Problem solved! All that trauma wouldnt've happened if it was as easy as a rejection. But Kyrex wanted his body so he decided to play pretend in the relationship.
Though, it's Diego's fault for continuing being in the relationship despite knowing what's happening though it's also Kyrex fault for being a terrible person. You can't deny that. Sure he had a bad childhood but instead of learning from it and becoming a better person, he decided to become a horrible person like his father! I pity him for that but that doesn't excuse his actions!